0.975 is correct, to get the answer you divide the length value by 10.
Answer and Explanation
Arranging the measured values in increasing order;
4.3s, 4.6s, 4.6s, 4.8s, 5.1s, 5.8s
The two outliers are obviously 4.3s and 5.8s; An outlier is a value in a statistical sample which does not fit a pattern that describes most other data point. Outliers make the average value complicated. So, it is usually better for data to be precise with data points spreading out around a small area.
So, the mean is the average of the four remaining data points after removing the outliers.
Mean = (4.6 + 4.6 + 4.8 + 5.1)/4
Mean = 4.775s
So, the value recorded should be 4.775s, 4.78s or 4.8s depending on the number of decimal places allowed.
QED!
Right, as you mentioned in the comments, you find 
by plugging in the different values of 
.
For 
, we have
Similarly, for 
, you get
